Intervertebral discs are found between the vertebral bodies which make up the spinal column. The intervertebral discs are fibrocartilaginous cushions that serve as spacers, shock absorbers and provide vertebral motion. The height of the disc maintains the distance of separation between the vertebral bodies, allowing for motion and room for spinal nerves to exit each spinal level with out being pinched or compressed. The disc serves as a shock absorber to protect the vertebrae, nerves and brain. The elasticity of the disc allows for vertebral motion. Intervertebral discs are composed of an annulus fibrosus and a nucleus pulposus. The annulus fibrosus encapsulates the inner nucleus pulposus portion of the disc. The annulus fibrosus is made up of concentric sheets of collagen fibers connected to the vertebral end plats. Both the annulus fibrosus and nucleus pulposus are composed of water, collagen and proteoglycans. Back pain is often caused by structural instability and dysfunction of the discs.
With the advent and increasing acceptance of artificial discs and the requirement for complete removal of an intervertebral disc or discectomy prior to insertion of an artificial disc, it will become increasingly important to be able to safely remove the entire intervertebral disc including the annulus fibrosus. Anterior discectomy is a dangerous procedure where the surgeon is operating very close to the spine and spinal tissue with instruments sharp enough to cut through the tough annulus fibrosus. Moreover, the disc is positioned between the vertebrae such that removal of the disc must be accomplished with minimal visibility when attempting to cut around the backside or posterior portion of the disc. The procedure of removing an entire disc will become a more frequent procedure, as replacement discs are now going through the approval process in the FDA and being introduced into the market.
Removal of the center portion, or nucleus pulposus, of the disc is known and has been used for several years to reduce back pain. Alternatively, fusion is used, which consists of removing portions of the problem disc and replacing it with a piece of bone taken from the patient's hip or a human cadaver. However, current surgical instrumentation, particularly, cutting instrumentation, are not adequate when performing complete removal of the disc, including removal of the annulus fibrosus of the disc. Currently available cutting instrumentation has a pointed sharp tip and can cause damage to vital blood vessels and the spinal tissue while removing the disc.
Several devices and instruments have been developed to be used in spinal surgery. U.S. Pat. No. 6,689,132 to Biscup (the '132 patent) discloses a spinal implant insertion tool. The tool facilitates in guiding and/or inserting one or more prosthetic implants into the intervertebral disc space. The insertion tool includes a body member and a curvilinear top portion connected to the body member. The top portion has a total angle of curvature of at least about 90% and a size and shape to enable over 50% of the top portion to be positioned within an outer perimeter of the intervertebral disc space. The tools can be provided in differently configured insertion tool set, which allows a surgeon to select the appropriate insertion tool that can be best used on a particular patient.
U.S. Pat. No. 6,599,291 to Foley et al. (the '291 patent) discloses methods and instruments for interbody surgical techniques, particularly methods and instruments for performing a surgical procedure in a disc space between adjacent vertebrae. The instruments include a distractor and a cutting instrument. The cutting instrument is positioned over the body portion and into the slots of the distractor so that the flanges are positioned between the cutting instrument and the adjacent tissue. This instrument provides for a number of cutters of increasing height to be used sequentially for removal of bony material from the vertebral endplates. Additionally, various shaped cutting edges can also be used, including flat cutting edges and rounded upper and lower cutting edges.
U.S. Pat. No. 6,228,022 to Friesem et al. (the '022 patent) discloses methods and instruments for spinal surgery, specifically, for preparing a disc space for implantation of a vertebral fusion or implant. The instrumentation includes a sleeve assembly with distraction fingers at one end to maintain distraction of a disc space. A switching sleeve having a pair of rotatable distractors is coupled within the outer sleeve, and the sleeves are placed over a dilator until the distractor heads are placed within the disc space. The dilator is withdrawn and the disc space distracted by rotating the distractors of the switching sleeve. The switching sleeve is uncoupled from the outer sleeve and the fingers of the outer sleeve are then inserted into the disc space. The switching sleeve and dilator are then removed and the outer sleeve defines a channel that allows insertion of implants at bilateral locations within the disc space without movement or manipulation of the outer sleeve.
U.S. Pat. No. 5,649,945 to Ray et al. (the '945 patent) discloses a spinal annulus cutter useful for cutting a multisided flap in an encapsulating ligament, such as an annulus of a disc, to provide access to an interior space. This instrument is not designed to be used in the removal of the entire disc, but rather is used in surgeries where the annulus is not removed. This surgical tool has the ability to pierce the annulus in such a way as to provide access to the discal area but allow for regenerative recover of the annular fibers afterwards, and prevent the damaging or destruction of the tightening or constraining ability of the annulus itself. The cutter is not designed to cut around the annulus.
U.S. Pat. No. 5,423,842 to Michelson (the '842 patent) discloses a spinal microknife. The knife was intended to simplify the procedure for performing an anterior cervical discectomy, while reducing the possibility of penetrating the dural sac or injuring the spinal cord. The microknife provides for an offset handle which allows unobstructed visualization of the cutting portion of the blade when operating on a cervical disc. The design of the blade tip has a smooth slightly biplanar convex bottom surface and a concave upper cutting surface, which will slip underneath the tissues to be cut, lifting the tissue onto the upper cutting portion of the blade which is perpendicular to the convex bottom surface. The tip of the knife is blunt to prevent puncturing. The knife is designed to allow for a safe way of cutting broadly across the posterior annulus or the posterior longitudinal ligament thus allowing full visualization of that space back there and the removal of any sequestered disc material under direct visualization.
U.S. Pat. No. 5,322,505 to Krause et al. (the '505 patent) discloses a powered arthroscopic surgical instrument, which includes a cutting implement disposed on the distal end of the inner tube. A region of the inner tube is flexible to enable the inner tube to accept the curvature imposed by the outer tube. The flexibility of the instrument allows the cutting tip to be manipulated into regions of the joint that cannot be reached by a straight instrument inserted through the same puncture.
U.S. Pat. No. 4,067,340 to LeNoir (the '340 patent) discloses a surgical instrument for meniscectomy. The instrument contains a pair of curved grooved guides of a shape corresponding to the periphery of the relatively inaccessible posterior portion of the meniscus. The cutting blade frame extends along the length of the grooved blade guide handles to the base of the two grooved guides and continues upward after being bent through an angle of approximately 100° with the cutting blade base mount. In operation, the flexible cutting blade advances along the grooves in the curved grooved guides and detaches the periphery of the meniscus near its base intra-articularly along a curved path corresponding to the shape of said curved grooved guides. This instrument is intended to replace both the Smillie and Lowe-Breck knives. The Smillie knives are a series of knives containing various angles which are used to perform a meniscectomy procedure on the knee.
One of the problems associated with the current surgical instruments that are used in the discectomy procedure is that they do not provide for the protection of other tissue structures near the intervertebral disc when the disc is being removed. Due to the great care that must be used in preventing any injury to tissue surrounding the intervertebral disc, such as the spinal cord, spinal tissue, nerve roots and iliac arteries and veins, safer cutting instruments are needed.
Additionally, there is a need for a surgical instrument that assists a surgeon in performing a discectomy, and specifically removing the annulus fibrosus, by following the curvature of the intervertebral disc as a guide. Such a cutting instrument would safely cut around the posterior portion of the disc where visibility is minimal, thus preventing injury to tissue surrounding the intervertebral disc. There is also a need for instruments that contains blunt blade guards to further prevent injury to surrounding tissue during the discectomy procedure and complete removal of the annulus fibrosus.
Alternatively, there is a need in the art for a set of cutting instruments for use in a discectomy procedure which when used sequentially, will safely cut around the tough annulus fibrosus of the intervertebral disc. Such instruments contain various curvatures that conform to various points around the circumference of the intervertebral disc.